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New diesel emission test equipment?

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What’s all the fuss about diesel emissions?

Jim Punter writes:
Should all MOT Testing Stations buy new Diesel Emission Test equipment (yet retaining their current diesel smoke meters) in the interests of public health? At MOT Testing we recently received the following article from Ralph Wilce, a member of the Westminster Commission for Road Air Quality (WCRAQ) and the chairman of its Air Monitoring Working Party. His organisation believes that the current MOT Smoke Meter test equipment should be supplemented by new advanced equipment to detect the smaller particles which are emitted if modern vehicles Diesel particulate filters are defective, tampered with, or removed. Here’s Wilce’s article…

Are MOT diesel smoke meters redundant?

By: Ralph Wilce

Not entirely! The current diesel MOT emission test was first used in the 1970s for vehicles without modern Diesel Particulate Filters (DPFs) and is now incapable of detecting excessive diesel emissions from modern engines which are fitted with DPFs, should the filters be defective, tampered with or removed. Yet current MOT smoke meters still comply with European and British legal requirements – so what is the problem? Surely if my diesel vehicle passes the MOT emission test, all is well. Well, that’s not necessarily so in terms of air quality and its threat to public health from modern vehicles fitted with DPFs.

A bit of history

Let’s delve into the archives. Some years ago, the British Government became convinced that diesel engines were preferable to petrol engines and used tax incentives to encourage motorists to switch to diesel powered vehicles. They believed diesel engines were better due to their higher fuel efficiencies and lower CO2 output. At the time there was little talk about the harmful effects of combustion generated pollutants such as particulate matter (PM – soot particles) and Oxides of Nitrogen (NOx). As awareness increased of the dangers to health of these harmful airborne pollutants, European regulations for type approval were tightened so all vehicles with diesel engines had to be fitted with a Diesel Particulate Filter. Ironically, a key issue was that as diesel engine efficiency increased, the carbon particles emitted in the exhaust became smaller and more likely to penetrate deep into people’s lungs, so deteriorating public health due to this pollution became a serious issue – hence DPFs.

When new European diesel emission regulations were introduced in 2009, many vehicle manufacturers had already started to fit particulate filters to reduce the level of Particulate Matter in diesel exhaust emission. Initially, at a vehicle’s Type Approval it was measured as Particle Mass and later in Particle Numbers per km. Using Particle Number metrics to European vehicle type approvals was an important milestone in recognition that the average size of soot particle from the tail pipe had become smaller, had little mass and presented a serious danger to public health.

Diesel particulate filters are highly efficient, typically removing more than 95% of all solid particles. Further, the filters are designed so that the walls catch all the harmful solid particles until the maximum filter capacity is reached. So-called regeneration is then triggered during which the soot particles are burned off and converted mainly into CO2.

Has the core been removed? There’s currently no way of telling without dismantling the DPF.

Detecting defective filters

But what happens when a Diesel Particulate Filter becomes defective or is deliberately manipulated or removed? Well, millions of dangerous particles are released instead of being filtered, even with the engine running at idle. During load and driving cycles, the difference between a working filter and one that lets the particles through is huge, and not at all apparent because the release of these very small particles is invisible to the naked eye but nevertheless has seriously damaging consequences to public health.

Barry Sheerman, MP, who is the chairman of the Westminster Commission for Road Air Quality (WCRAQ), an independent Group working to shape and develop legislation to improve the quality of the air we breathe, commented; ‘If a DPF is faulty, a single vehicle can produce the same (health damaging) pollution as a three-lane, 360-mile-long traffic jam of vehicles with compliant filters. That is the distance from Huddersfield to Land’s End. Shocked?

…If a DPF is faulty, a single vehicle can produce the same (health damaging) pollution as a three-lane, 360-mile-long traffic jam of vehicles with compliant filters. That is the distance from Huddersfield to Land’s End…

Blind smokemeters

Yet these faulty DPFs cannot be identified during an MOT diesel emission test. Why not? Well, the technology used by the smoke meter is not sensitive enough to detect the small-sized particles emitted from modern diesel engines when the filter is no longer working properly. The current diesel smoke meter uses light absorption by the particles to measure the amount of smoke. But the smaller particles in modern engines absorb hardly any light, so even vehicles with a defective DPF typically show a reading close to zero. The current MOT smoke meter technology just can’t ‘see’ these particles, it is blind to their existence and therefore, no longer fit for purpose in checking the effectiveness of DPFs. Yet there is increasing evidence to substantiate the dangers of these small soot particles to our health.

Cancer causing particles

Diesel engine exhaust was first classified as carcinogenic by the World Health Organisation in 2012. Research has shown that the chemical coatings on the soot particles can be a cancer trigger and Dr Andreas Mayer, an acknowledged expert in this area has explained during one of our recent WCRAQ meetings about the harmful effects of such coatings called PAHs (Polycyclic Aromatic Hydrocarbons) that are found on diesel soot particles. Not only are the particles small enough to penetrate deep into our respiratory system, but such combustion generated nanoparticles are likely to cross into the blood and be carried to areas of disease or promote life-shortening diseases.

So here’s the problem – more efficient diesel engines generate smaller emitted particles in the exhaust, which if released cause more danger to health. Those particles whilst virtually eliminated by efficient diesel particulate filters are undetectable by MOT smoke meters if the filter failed, was tampered with, or removed completely. So, what can be done to stop this ‘invisible killer’?

Modern diesel emission equipment

There are now more sensitive diesel emission MOT Test equipment on the market called Particle Number Counters (PNCs), that detects defective DPFs and if they have been removed or tampered with. This equipment counts the number of particles in a cubic centimetre at the tailpipe during an idle test to see whether the filter is working efficiently. If the filter allows too many particles through, then the filter is rejected, and the vehicle needs to be repaired or removed from the road. Such equipment would be very effective if used by Britain’s MOT Testing garages.

Such DPF control tests are now being introduced as part of the MOT inspection in several European countries including the Netherlands, Belgium, Germany, and Switzerland to ensure diesel vehicles fitted with DPFs remain in-service compliant during their life cycle.

Using Dutch Government research and analysis, it is estimated that in the UK, more than 1,000 tonnes of these small particles are pumped into the air we breathe because of faulty DPFs (around 10% of the total diesel engine powered cars and commercial vehicles on our roads). So public health is endangered, and people are going to become ill as a result, but can that cost be counted? Yes, it can…

Counting the cost

To calculate the external cost of PM in terms of avoidable cost of healthcare, the Dutch attribute €536 per kg for traffic in highly urbanized areas and €129 per kg for traffic in rural areas. Assuming a 25% to 75% split re rural/urban areas, the weighted average is €231 per kg for the UK. It is estimated that the environmentally beneficial effect of introducing DPF control in the UK is a reduction in PM emissions of 1,000 tonnes. The social benefit from cleaner air is therefore, €231 x (1,000 * 1,000) = €231 million or approximately £200 million at today’s exchange rates, per year!

Identifying and removing high emitting vehicles through the MOT Scheme this way is key, especially to urban air quality improvement and the main reason the WCRAQ is lobbying parliament for the UK to follow suit by using particle counting technology in diesel test meters at MOT Testing Stations.

With the pricing of these new particle number counters being similar to gas and smoke meters, the WCRAQ argues that we must improve the ‘here and now’ whilst also encouraging a migration to environmentally more friendly and sustainable energies for transport. After all, the current large diesel fleet will be with us for many years to come, given the average lifetime of vehicles and the likelihood that commercial vehicles will remain diesel-fuelled.

Let’s ensure that the strict emission standards are not just for type approvals but also for the lifetime of the vehicle.


One final thought, Gasoline Particulate filters (GPFs) have been fitted to petrol vehicles for vehicle type approval since 2017. Research is showing that PN emissions from petrol engines also need to be monitored over time, which means the effectiveness of such filters also needs to be checked during MOT Testing in the future. This is the reason those countries now mandating DPF control using Particle Number Counters are already planning for the introduction of GPF control of petrol-powered vehicles using the same devices.

Ralph Wilce is the chairman of the Air Monitoring Working Party of the  Westminster Commission for Road Air Quality (WCRAQ).

So, what do we at MOT Testing think about Ralph’s article?
1. Public health
Clearly, purely in terms of public health we should be using particle counting equipment for our diesel emissions test in Testing Stations.
2. What does DVSA think?
DVSA provided us with this official response.
“DVSA’s priority is to help everyone keep their vehicle safe to drive. This includes measures to protect the public from harmful vehicle emissions. Work is ongoing to determine the best direction for vehicle emissions. This includes looking at new equipment, but we will need to be careful in balancing cost to garages against the potential benefits.”
3. Cost benefit
For Testing Stations this would mean they will need three different pieces of equipment to test emissions. The current two analysers plus a new device which counts particles from vehicles mandatorily fitted with Diesel Particulate Filters. We contacted Julian Woods, the Chief Executive of the Garage Equipment Association as to the price of diesel particle counting equipment. He said, “…between £5,000 to £10,000 depending on the accuracy required”.
So at approximately £7,500 each*, if every Test Station had to purchase a new meter the cost would be £176.M (approx 23,500 Testing Stations) – a large proportion of the first year’s saving due to improved public health, although it would be a one-off cost which would need to be re-couped by an increase in the MOT fee – which would not be popular amongst motorists. On an ongoing basis there will also be regular maintenance costs for the new equipment. Nevertheless, improved public health should take precedence – although whether or not the Government will see it that way and increase the MOT fee to cover the additional costs is unlikely if previous experience is anything to go by. Another factor is that with the increased popularity of electric cars, and those with internal combustion engines to be unavailable after 2030, the benefit will attenuate over time.
* Ralph Wilce also notes, “there’s also the extra revenue generated by the repairs for the workshop and the improvements to CO2 output, and fuel efficiency as vehicles are better maintained to increase the life of the DPF… in Holland the equipment (already in use) costs about £5,000”
4. Parliamentary mandate
Barry Sheerman, MP, who is the chairman of the Westminster Commission for Road Air Quality (WCRAQ) has submitted a Bill in Parliament to mandate the new Diesel emissions equipment, and it recently passed its first reading.

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